Battery having a low output voltage

ABSTRACT

An electrochemical battery cell comprising an anode having a primary anode active material, a cathode, and an ion-conducting electrolyte, wherein the cell has an initial output voltage, Vi, measured at 10% depth of discharge (DoD), selected from a range from 0.3 volts to 0.8 volts, and a final output voltage Vf measured at a DoD no greater than 90%, wherein a voltage variation, (Vi−Vf)/Vi, is no greater than ±10% and the specific capacity between Vi and Vf is no less than 100 mAh/g or 200 mAh/cm3 based on the cathode active material weight or volume, and wherein the primary anode active material is selected from lithium (Li), sodium (Na), potassium (K), magnesium (Mg), aluminum (Al), zinc (Zn), titanium (Ti), manganese (Mn), iron (Fe), vanadium (V), cobalt (Co), nickel (Ni), a mixture thereof, an alloy thereof, or a combination thereof.

FIELD OF THE INVENTION

The present invention relates generally to the field of electrochemicalbattery and, more particularly, to a battery that naturally supplies anexternal circuit with an output voltage from 0.3 volts to 0.8 voltswithout using a voltage regulator (e.g. voltage reducer or transformer).

BACKGROUND OF THE INVENTION

The emergence of “Internet-of-Things” and next-generation sensortechnologies for health monitoring and artificial intelligenceapplications demands the availability of batteries that last for manydecades without recharging and, in particular, that enable wireless,wearable, or implanted devices to become maintenance-free withoutreplacing the batteries.

Using sensors as an example, it has been determined that the ultra lowpower monitoring sensor requires low-voltage power sources that canoperate between 0.3 and 0.8 V without using a voltage reducer. A loweroperating voltage means a lower power consumption rate. The use of avoltage reducer (e.g. a transformer) would mean additional power lossand must be avoided. However, commercially available battery systems areall voltage-mismatched, such as lithium-ion (3.7 V), lead acid (2 V),zinc-carbon/alkaline (1.5 V), zinc-air (1.4 V), and nickel-metal (1.2V), which would require a voltage reducing circuit to bring theoperating voltage to below 0.8 volts. Furthermore, most of thesebatteries are poor in energy density for lifelong functioning.Additionally, since the size of remote wireless sensors is tiny in mostcases, the volumetric energy density of a battery is especiallyimportant for sensor devices.

Thus, an urgent need exists for a long-lasting primary battery thatoperates in a voltage range from 0.3 volts to 0.8 volts and suppliespower to a wireless, wearable, or implanted device without using avoltage reducer circuit. Preferably, such a battery system should alsoallow for flexibility in adjusting the output voltage in response to thevarious device power design needs.

SUMMARY OF THE INVENTION

Herein reported is an electrochemical battery cell that meets theaforementioned requirements. The battery cell comprises:

(A) an anode having a primary anode active material,

(B) a cathode having a primary cathode active material, and

(C) an ion-conducting electrolyte in ionic contact with the anode andthe cathode,

wherein the cell has an initial output voltage, Vi, measured at 10%depth of discharge (DoD), from a lower limit of 0.3 volts to an upperlimit of 0.8 volts, and a final output voltage Vf measured at a DoD nogreater than 90%, wherein a voltage variation, (Vi−Vf)/Vi, is no greaterthan ±10% (preferably no greater than ±5%) and the specific capacitybetween Vi and Vf is no less than 100 mAh/g or 200 mAh/cm³ based on thecathode active material weight or volume, and wherein the anode containslithium (Li), sodium (Na), potassium (K), magnesium (Mg), aluminum (Al),zinc (Zn), titanium (Ti), manganese (Mn), iron (Fe), vanadium (V),cobalt (Co), nickel (Ni), a mixture thereof, an alloy thereof, or acombination thereof as the primary anode active material. The preferredanode active materials are Li, Na, Mg, Al and their alloys or mixtures.

The depth of discharge (DoD) is a term well-known in the art of battery.In short, the DoD is the ratio of the actual discharge amount (specificcapacity, in terms of mAh/g or mAh/cm³) to the maximum discharge amountthat a battery cell can provide in terms of the cell weight, the anodeactive material weight, or the cathode active material weight. Forexample, if metal M (as a cathode active material) relative to Li (as ananode active material, having a sufficient amount to match M) can storeup to 1000 mAh of Li ions per gram of M, and this Li/M cell is onlyallowed to discharge to 900 mAh/g, then this specific capacity of 900mAh/g corresponds to a DoD of 900/1,000=90%.

When measured at 10% depth of discharge (DoD), the battery cell mustdeliver an initial output voltage Vi from 0.3 volts to 0.8 volts,preferably from 0.3 volts to 0.7 volts. The battery cell also delivers afinal output voltage Vf measured at a DoD no greater than 90% and thespecific capacity between Vi and Vf is preferably no less than 100 mAh/gor 200 mAh/cm³ based on the cathode active material weight or volume.Preferably, the voltage variation, (Vi−Vf)/Vi, is no greater than ±10%(further preferably no greater than ±5%) between Vi and the selected Vf.A battery designer or electronic device designer is free to select a Vfat a DoD from 10% to 90%, but the specific capacity delivered by thebattery cell between Vi and Vf is preferably no less than 100 mAh/g or200 mAh/cm³ based on the cathode active material weight or volume.

The electrochemical battery cell may further comprise an anode currentcollector supporting the anode and/or a cathode current collectorsupporting the cathode.

The primary cathode active material may be selected from a metal,semi-metal, or non-metal element different than the primary anode activematerial and the metal, semi-metal, or non-metal element in the cathodeis selected from tin (Sn), bismuth (Bi), antimony (Sb), indium (In),tellurium (Te), magnesium (Mg), aluminum (Al), zinc (Zn), titanium (Ti),manganese (Mn), iron (Fe), vanadium (V), cobalt (Co), nickel (Ni),selenium (Se), sulfur (S), a mixture thereof, an alloy thereof, or acombination thereof. The metal, semi-metal, or non-metal used as theprimary cathode active material must be different than the metal used asthe primary anode active material and, when coupled with the primaryanode active material, must be able to deliver an output voltage in therange of 0.3 volts to 0.8 volts.

The primary cathode active material may also be selected from a metaloxide, metal phosphate, or metal sulfide; in particular, it may beselected from a tin oxide, cobalt oxide, nickel oxide, manganese oxide,vanadium oxide, iron phosphate, manganese phosphate, vanadium phosphate,transition metal sulfide, or a combination thereof.

In certain embodiments, the primary cathode active material contains aninorganic material selected from carbon sulfur, sulfur compound, lithiumpolysulfide, transition metal dichalcogenide, a transition metaltrichalcogenide, or a combination thereof.

The electrolyte may be selected from an aqueous, organic, polymeric,ionic liquid, quasi-solid, or solid-state electrolyte.

Preferably, the anode further contains graphene as a protective materialto protect the primary anode active material. Further preferably, theprimary anode active material is embraced by graphene sheets or embeddedin a graphene film, graphene paper, graphene mat, or graphene foam.

The graphene material for use in the anode and/or the cathode maycontain a pristine graphene material having less than 0.01% by weight ofnon-carbon elements or a non-pristine graphene material having 0.01% to50% by weight of non-carbon elements, wherein said non-pristine grapheneis selected from graphene oxide, reduced graphene oxide, graphenefluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, boron-doped graphene,nitrogen-doped graphene, chemically functionalized graphene, or acombination thereof.

In certain embodiments, the primary cathode active material is embracedby graphene sheets or embedded in a graphene film, graphene paper,graphene mat, or graphene foam. Preferably, the primary anode activematerial in the anode is embraced by graphene sheets or embedded in agraphene film, graphene paper, graphene mat, or graphene foam and theprimary cathode active material in the cathode is embraced by graphenesheets or embedded in a graphene film, graphene paper, graphene mat, orgraphene foam.

In the presently invented battery cell, the graphene film, graphenepaper, graphene mat, or graphene foam (having the primary anode activematerial embedded therein) in the anode is connected to a first batteryterminal tab (i.e. the graphene film, paper, mat, or foam itself servingas an anode current collector) and there is no separate or additionalanode current collector (e.g. Cu foil) to support the graphene film,graphene paper, graphene mat, or graphene foam. This feature cansignificantly reduce the battery weight and volume.

In certain embodiments, the graphene film, graphene paper, graphene mat,or graphene foam in the cathode having the primary cathode activematerial embedded therein is connected to a battery terminal tab (thegraphene film, graphene paper, graphene mat, or graphene foam itselfacting as a cathode current collector) and there is no separate oradditional cathode current collector to support the graphene film,graphene paper, graphene mat, or graphene foam.

Most preferably, the graphene film, graphene paper, graphene mat, orgraphene foam in the anode (having a first terminal tab connectedthereto) serves as the anode current collector (no additional orseparate anode current collector such as Cu foil) and the graphene film,graphene paper, graphene mat, or graphene foam in the cathode (having asecond battery terminal tab connected thereto) serves as the cathodecurrent collector and there is no separate or additional cathode currentcollector (such as Al foil) to support said graphene film, graphenepaper, graphene mat, or graphene foam in the cathode. This feature cansignificantly reduce the battery weight and volume.

Furthermore, the flexibility of the graphene film, graphene paper,graphene mat, or graphene foam in both the anode and the cathode alsoenables the production of flexible battery cell for use in a wireless,wearable, or implanted device that can be of odd shape.

Preferably, the specific capacity between Vi and Vf is no less than 200mAh/g or 400 mAh/cm³ (more preferably no less than 300 mAh/g or 600mAh/cm³ and further preferably no less than 400 mAh/g or 800 mAh/cm³)based on the cathode active material weight or volume.

In certain embodiments, the cathode further contains graphene as anelectrochemical property modifier to the primary cathode active materialwherein the added graphene increases the cell specific capacity, orincreases or decreases a cell output voltage (relative to acorresponding cell without the added graphene in the cathode).Preferably, the primary cathode active material is bonded to orphysically supported by a surface of graphene. The graphene may containa pristine graphene material having less than 0.01% by weight ofnon-carbon elements or a non-pristine graphene material having 0.01% to50% by weight of non-carbon elements, wherein the non-pristine grapheneis selected from graphene oxide, reduced graphene oxide, graphenefluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, boron-doped graphene,nitrogen-doped graphene, chemically functionalized graphene, or acombination thereof.

The present invention also provides an electronic device containing thepresently invented electrochemical battery cell as a power source. Theelectronic device may contain a sensor, a wireless device, a wearabledevice, or a medical device electronically connected to the inventedelectrochemical battery cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) schematic of a prior art lithium metal battery cell (e.g. aprimary cell), composed of an anode current collector (e.g. Cu foil), asheet of Li metal foil as the anode layer (Li metal being the anodeactive material), a porous separator, a cathode active material layercomposed of particles of a cathode active material (e.g. MoS₂ or MnO₂)mixed with a conductive filler (e.g. acetylene black) and a resin binder(e.g. PVDF), and a cathode current collector (e.g. Al foil);

FIG. 1(B) schematic of a prior art lithium-ion battery cell (a secondaryor rechargeable cell), composed of an anode current collector (e.g. Cufoil), an anode layer composed of particles of an anode active material(e.g. graphite or Si particles) mixed with a conductive filler (e.g.carbon black) and a resin binder (e.g. SBR), a porous separator, acathode active material layer composed of particles of a cathode activematerial (e.g. LiCoO₂ or LiFePO₄) mixed with a conductive filler and aresin binder (e.g. PVDF), and a cathode current collector (e.g. Alfoil).

FIG. 2 A flow chart illustrating various prior art processes ofproducing exfoliated graphite products (flexible graphite foils andexpanded graphite flakes), along with a process for producing pristinegraphene foam 40 a or graphene oxide foams 40 b.

FIG. 3 Illustrative examples showing the discharge curves (voltage vs.DoD curves, or voltage vs. time at a constant current density) of twohypothetical battery cells: Cell A has a total specific capacity of1,500 mAh/cm³ (from 0% DoD to 100% DoD) and Cell B has a specificcapacity of 600 mAh/cm³.

FIG. 4 A possible graphene sheet-to-sheet merging mechanism.

FIG. 5 The discharge curve (voltage vs. DoD) of a low-voltage Al—S cell.

FIG. 6 The discharge curves (voltage vs. DoD) of a low-voltage Li—P celland a graphene modified Li—P/graphene cell.

FIG. 7 The discharge curve (voltage vs. DoD) of a low-voltage Li—SnO₂cell.

FIG. 8 The discharge curve (voltage vs. DoD) of a low-voltage Na—SnO₂cell.

FIG. 9 The discharge curve (voltage vs. DoD) of a low-voltage Li—Sbcell.

FIG. 10 The discharge curve (voltage vs. DoD) of a low-voltage Na—Sbcell.

FIG. 11 The discharge curve (voltage vs. DoD) of a low-voltage Li—Fe₃O₄cell.

FIG. 12 The discharge curve (voltage vs. DoD) of a low-voltage Na—Fe₃O₄cell.

FIG. 13 The discharge curve (voltage vs. DoD) of a low-voltage Li—Sncell.

FIG. 14 The discharge curves (voltage vs. DoD) of a low-voltage Li—Mn₃O₄cell and a graphene-modified cell (Li—Mn₃O₄/graphene cell).

FIG. 15 The discharge curve (voltage vs. DoD) of a low-voltage Li—Alcell.

FIG. 16 The discharge curve (voltage vs. DoD) of a low-voltage Li—MoO₃cell.

FIG. 17 The discharge curve (voltage vs. DoD) of a low-voltage Li—MoS₂cell.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a conventional primary cell configuration, as illustrated in FIG.1(A), the cell is typically composed of an anode current collector (e.g.Cu foil), a sheet of Li metal foil as the anode layer (Li metal beingthe anode active material), a porous separator, a cathode activematerial layer composed of particles of a cathode active material (e.g.MoS₂ or MnO₂) mixed with a conductive filler (e.g. acetylene black) anda resin binder (e.g. PVDF), and a cathode current collector (e.g. Alfoil. The anode active material (e.g. Li metal) can be in a thin filmform deposited directly onto the anode current collector, such as asheet of copper foil.

However, such a lithium metal battery cell is normally designed todeliver a high output voltage (e.g. >2.0 volts and more typically >3.0volts) since essentially all the current electronic devices, powertools, electric vehicles, etc. operate at a cell voltage higher than 1.0volts. Other types of batteries, primary or secondary, are alsotypically designed and built to provide an output voltage significantlyhigher than 1.0 volt; e.g. lithium-ion (3.7 V), lead acid (2 V),alkaline (1.5 V), zinc-air (1.4 V), and nickel-metal hydride (1.2 V). Adevice operating at a higher voltage than 4.0 volts requires the use ofmultiple cells connected in series (e.g. an electric bike operating on12 volts requires 6 lead acid battery cells connected in series).

As illustrated in FIG. 1(B), a lithium-ion battery cell (a secondary orrechargeable cell) is typically composed of an anode current collector(e.g. Cu foil), an anode or negative electrode, a porous separatorand/or an electrolyte component, a cathode electrode (typicallycontaining a cathode active material, a conductive additive, and a resinbinder), and a cathode current collector (e.g. Al foil). In a morecommonly used cell configuration, the anode layer is composed ofparticles of an anode active material (e.g. graphite, Sn, SnO₂, or Si),a conductive additive (e.g. carbon black particles), and a resin binder(e.g. SBR or PVDF).

Cu foil in the anode and Al foil in the cathode are each attached(welded or soldered) with a terminal tab for connection to an externalcircuit. However, these current collectors add weight and volume to thecell, reducing the effective gravimetric and volumetric energy densitiesof the cell.

The ultra low-power monitoring sensors require the availability oflow-voltage power sources operating at a voltage level in the range of0.3-0.8 V. This voltage level preferably remains relatively constantover a long operating period of time. Further, most of the wireless,wearable, or implanted devices require the power source to be as smallin sizes as possible. Prior art batteries, either primary or secondary,do not meet these requirements.

These issues are herein addressed by the instant invention. Oneembodiment of the instant invention is an electrochemical battery cellthat meets the aforementioned requirements. The battery cell comprises:(A) an anode having a primary anode active material; (B) a cathodehaving a primary cathode active material, and (C) an ion-conductingelectrolyte in ionic contact with the anode and the cathode, wherein thecell has an initial output voltage, Vi, measured at 10% depth ofdischarge (DoD), from a lower limit of 0.3 volts to an upper limit of0.8 volts, and a final output voltage Vf measured at a DoD no greaterthan 90%, wherein a voltage variation, (Vi−Vf)/Vi, is no greater than±15% (preferably no greater than ±10% and further preferably no greaterthan ±5%) and the specific capacity between Vi and Vf is no less than100 mAh/g or 200 mAh/cm³ based on the cathode active material weight orvolume, and wherein the anode contains lithium (Li), sodium (Na),potassium (K), magnesium (Mg), aluminum (Al), zinc (Zn), titanium (Ti),manganese (Mn), iron (Fe), vanadium (V), cobalt (Co), nickel (Ni), amixture thereof, an alloy thereof, or a combination thereof as theprimary anode active material. The preferred anode active materials areLi, Na, Mg, Al and their alloys.

The depth of discharge (DoD) is the ratio of the actual discharge amount(specific capacity, mAh/g or mAh/cm³) to the maximum discharge amountthat a battery cell can provide in terms of the cell weight, the anodeactive material weight, or the cathode active material weight. FIG. 3provides illustrative examples showing the discharge curves (voltage vs.DoD curves, or voltage vs. time curves at a constant current density) oftwo cells: Cell A has a total specific capacity of 1,500 mAh/cm³ (from0% DoD to 100% DoD) and Cell B has a specific capacity of 600 mAh/cm³.

For Cell A in FIG. 3, the 10% DoD occurs at 150 mAh/cm³ and 90% DoD at1,350 mAh/cm³. The most useful DoD range, from 10% to 90%, correspondsto a specific capacity of 1,200 mAh/cm³. With an average voltage of 0.55volts, this range delivers an energy density of 1,200×0.55=660 Wh/cm³(based on the cathode volume), which is acceptable, albeit notexceptional, for use in a lower power device. Further, from 10% to 90%DoD, the voltage drops from 0.575 volts to 0.545 volts, a variation of(0.575−0.545)/0.575=5.2%.

For Cell B, the 10% DoD occurs at 60 mAh/cm³ and 90% DoD at 540 mAh/cm³.This range corresponds to a specific capacity of 480 mAh/cm³. However,over this range, the voltage drops from 0.50 to 0.33 volts, a variationof (0.50−0.33)/0.50=34%, which is not acceptable. The electronic devicenormally requires a relatively stable voltage over the useful lifetime.It is reasonable to assume that a variation of ±10% is acceptable; then,the voltage cannot be allowed to drop from 0.50 to below 0.45 volts overa desired range of DoD. For Cell B, this 0.45 volts corresponds to a DoDof 35%. Consequently, the useful voltage range is from 10% to 35% DoD,corresponding to a useful specific capacity of (35%−10%)×600=150mAh/cm³, which is too low for any practical use as a long-life primarycell.

Thus, in summary, when measured at 10% depth of discharge (DoD), thebattery cell must deliver an initial output voltage Vi from 0.3 volts to0.8 volts, preferably from 0.3 volts to 0.7 volts. The battery cell alsodelivers a final output voltage Vf measured at a DoD no greater than 90%and the specific capacity between Vi and Vf is preferably no less than100 mAh/g or 200 mAh/cm³ based on the cathode active material weight orvolume. Preferably, the voltage variation, (Vi−Vf)/Vi, is no greaterthan ±10% (more preferably no greater than ±5%) between Vi and theselected Vf. A battery designer or electronic device designer is free toselect a Vf at a DoD from 10% to 90%, but the specific capacitydelivered by the battery cell between Vi and Vf is preferably no lessthan 200 mAh/g or 400 mAh/cm³ based on the cathode active materialweight or volume (further preferably no less than 300 mAh/g or 600mAh/cm³, more preferably no less than 400 mAh/g or 800 mAh/cm³, evenmore preferably no less than 500 mAh/g or 1,000 mAh/cm³, still furtherpreferably no less than 700 mAh/g or 1,400 mAh/cm³, and most preferablyno less than 1,000 mAh/g or 2,000 mAh/cm³).

The primary cathode active material may be selected from a metal,semi-metal, or non-metal element different than the primary anode activematerial and the metal, semi-metal, or non-metal element in the cathodeis selected from tin (Sn), bismuth (Bi), antimony (Sb), indium (In),tellurium (Te), phosphor (P), magnesium (Mg), aluminum (Al), zinc (Zn),titanium (Ti), manganese (Mn), iron (Fe), vanadium (V), cobalt (Co),nickel (Ni), selenium (Se), sulfur (S), a mixture thereof, an alloythereof, or a combination thereof. The metal, semi-metal, or non-metalused as the primary cathode active material must be different than themetal used as the primary anode active material and, when coupled withthe primary anode active material, must deliver an output voltage in therange of 0.3 volts to 0.8 volts.

The primary cathode active material may also be selected from a metaloxide, metal phosphate, or metal sulfide; in particular, it may beselected from a tin oxide, cobalt oxide, nickel oxide, manganese oxide,vanadium oxide, iron phosphate, manganese phosphate, vanadium phosphate,transition metal sulfide, or a combination thereof.

In certain embodiments, the primary cathode active material contains aninorganic material selected from carbon sulfur, sulfur compound, lithiumpolysulfide, transition metal dichalcogenide, a transition metaltrichalcogenide, or a combination thereof.

The electrochemical battery cell may further comprise an anode currentcollector supporting the anode and/or a cathode current collectorsupporting the cathode.

Preferably, the anode and/or cathode further contain graphene as aprotective material to protect the primary anode/cathode activematerial. Further preferably, the primary anode active material and/orcathode active material are embraced by graphene sheets or embedded in agraphene film, graphene paper, graphene mat, or graphene foam.

The graphene material for use in the anode and/or the cathode maycontain a pristine graphene material having less than 0.01% by weight ofnon-carbon elements or a non-pristine graphene material having 0.01% to50% by weight of non-carbon elements, wherein said non-pristine grapheneis selected from graphene oxide, reduced graphene oxide, graphenefluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, boron-doped graphene,nitrogen-doped graphene, chemically functionalized graphene, or acombination thereof.

In the presently invented battery cell, the graphene film, graphenepaper, graphene mat, or graphene foam (having the primary anode activematerial embedded therein) in the anode is connected to a first batteryterminal tab (i.e. the graphene film, paper, mat, or foam itself servingas an anode current collector) and there is no separate or additionalanode current collector (e.g. Cu foil) to support the graphene film,graphene paper, graphene mat, or graphene foam. This feature cansignificantly reduce the battery weight and volume and, as such,significantly increase the gravimetric and volumetric energy density.

In certain embodiments, the graphene film, graphene paper, graphene mat,or graphene foam in the cathode having the primary cathode activematerial embedded therein is connected to a battery terminal tab (thegraphene film, graphene paper, graphene mat, or graphene foam itselfacting as a cathode current collector) and there is no separate oradditional cathode current collector to support the graphene film,graphene paper, graphene mat, or graphene foam.

Most preferably, both the anode and the cathode sides do not have aseparate (additional) current collector. Specifically, the graphenefilm, graphene paper, graphene mat, or graphene foam in the anode(having a first terminal tab connected thereto) serves as the anodecurrent collector (no additional or separate anode current collectorsuch as Cu foil) and the graphene film, graphene paper, graphene mat, orgraphene foam in the cathode (having a second battery terminal tabconnected thereto) serves as the cathode current collector and there isno separate or additional cathode current collector (such as Al foil) tosupport said graphene film, graphene paper, graphene mat, or graphenefoam in the cathode. This feature can significantly reduce the batteryweight and volume and, as such, further significantly increase thegravimetric and volumetric energy density.

Furthermore, the flexibility of the graphene film, graphene paper,graphene mat, or graphene foam in both the anode and the cathode and thelack of Cu foil and Al foil current collectors also enables theproduction of flexible battery cell for use in a wireless, wearable, orimplanted device that can be of an odd shape. These unexpected featuresare highly desirable for wireless, wearable, or implanted devices.

Another unexpected feature of instant invention is the notion thatgraphene is capable of modifying the electrochemical properties of ananode or a cathode active material (e.g. changing the discharge curve).Thus, in certain embodiments, the cathode further contains graphene asan electrochemical property modifier to the primary cathode activematerial wherein the added graphene increases the cell specificcapacity, or increases or decreases a cell output voltage (relative to acorresponding cell without the added graphene in the cathode).Preferably, the primary cathode active material is bonded to orphysically supported by a surface of graphene. Again, the graphene, asan electrochemical modifier, may contain a pristine graphene materialhaving less than 0.01% by weight of non-carbon elements or anon-pristine graphene material having 0.01% to 50% by weight ofnon-carbon elements, wherein the non-pristine graphene is selected fromgraphene oxide, reduced graphene oxide, graphene fluoride, graphenechloride, graphene bromide, graphene iodide, hydrogenated graphene,nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene,chemically functionalized graphene, or a combination thereof.

Bulk natural graphite is a 3-D graphitic material with each graphiteparticle being composed of multiple grains (a grain being a graphitesingle crystal or crystallite) with grain boundaries (amorphous ordefect zones) demarcating neighboring graphite single crystals. Eachgrain is composed of multiple graphene planes that are oriented parallelto one another. A graphene plane in a graphite crystallite is composedof carbon atoms occupying a two-dimensional, hexagonal lattice. In agiven grain or single crystal, the graphene planes are stacked andbonded via van der Waal forces in the crystallographic c-direction(perpendicular to the graphene plane or basal plane). Although all thegraphene planes in one grain are parallel to one another, typically thegraphene planes in one grain and the graphene planes in an adjacentgrain are inclined at different orientations. In other words, theorientations of the various grains in a graphite particle typicallydiffer from one grain to another.

The constituent graphene planes of a graphite crystallite in a naturalor artificial graphite particle can be exfoliated and extracted orisolated to obtain individual graphene sheets of carbon atoms providedthe inter-planar van der Waals forces can be overcome. An isolated,individual graphene sheet of carbon atoms is commonly referred to assingle-layer graphene. A stack of multiple graphene planes bondedthrough van der Waals forces in the thickness direction with aninter-graphene plane spacing of approximately 0.3354 nm is commonlyreferred to as a multi-layer graphene. A multi-layer graphene platelethas up to 300 layers of graphene planes (<100 nm in thickness), but moretypically up to 30 graphene planes (<10 nm in thickness), even moretypically up to 20 graphene planes (<7 nm in thickness), and mosttypically up to 10 graphene planes (commonly referred to as few-layergraphene in scientific community). Single-layer graphene and multi-layergraphene sheets are collectively called “nano graphene platelets”(NGPs). Graphene or graphene oxide sheets/platelets (collectively, NGPs)are a new class of carbon nano material (a 2-D nano carbon) that isdistinct from the 0-D fullerene, the 1-D CNT, and the 3-D graphite.

Our research group pioneered the development of graphene materials andrelated production processes as early as 2002: (1) B. Z. Jang and W. C.Huang, “Nano-scaled Graphene Plates,” U.S. Pat. No. 7,071,258 (Jul. 4,2006), application submitted on Oct. 21, 2002; (2) B. Z. Jang, et al.“Process for Producing Nano-scaled Graphene Plates,” U.S. patentapplication Ser. No. 10/858,814 (Jun. 3, 2004); and (3) B. Z. Jang, A.Zhamu, and J. Guo, “Process for Producing Nano-scaled Platelets andNanocomposites,” U.S. patent application Ser. No. 11/509,424 (Aug. 25,2006).

In one process, graphene materials are obtained by intercalating naturalgraphite particles with a strong acid and/or an oxidizing agent toobtain a graphite intercalation compound (GIC) or graphite oxide (GO),as illustrated in FIG. 2 (a process flow chart). The presence ofchemical species or functional groups in the interstitial spaces betweengraphene planes serves to increase the inter-graphene spacing (d₀₀₂, asdetermined by X-ray diffraction), thereby significantly reducing the vander Waals forces that otherwise hold graphene planes together along thec-axis direction. The GIC or GO is most often produced by immersingnatural graphite powder (20 in FIG. 2) in a mixture of sulfuric acid,nitric acid (an oxidizing agent), and another oxidizing agent (e.g.potassium permanganate or sodium perchlorate). The resulting GIC (22) isactually some type of graphite oxide (GO) particles if an oxidizingagent is present during the intercalation procedure. This GIC or GO isthen repeatedly washed and rinsed in water to remove excess acids,resulting in a graphite oxide suspension or dispersion, which containsdiscrete and visually discernible graphite oxide particles dispersed inwater. In order to produce graphene materials, one can follow one of thetwo processing routes after this rinsing step, briefly described below:

Route 1 involves removing water from the suspension to obtain“expandable graphite,” which is essentially a mass of dried GIC or driedgraphite oxide particles. Upon exposure of expandable graphite to atemperature in the range of typically 800-1,050° C. for approximately 30seconds to 2 minutes, the GIC undergoes a rapid volume expansion by afactor of 30-300 to form “graphite worms” (24), which are each acollection of exfoliated, but largely un-separated graphite flakes thatremain interconnected.

In Route 1A, these graphite worms (exfoliated graphite or “networks ofinterconnected/non-separated graphite flakes”) can be re-compressed toobtain flexible graphite sheets or foils (26) that typically have athickness in the range of 0.1 mm (100 μm)-0.5 mm (500 μm).Alternatively, one may choose to use a low-intensity air mill orshearing machine to simply break up the graphite worms for the purposeof producing the so-called “expanded graphite flakes” (49) which containmostly graphite flakes or platelets thicker than 100 nm (hence, not anano material by definition).

In Route 1B, the exfoliated graphite is subjected to high-intensitymechanical shearing (e.g. using an ultrasonicator, high-shear mixer,high-intensity air jet mill, or high-energy ball mill) to form separatedsingle-layer and multi-layer graphene sheets (collectively called NGPs,33), as disclosed in our U.S. application Ser. No. 10/858,814.Single-layer graphene can be as thin as 0.34 nm, while multi-layergraphene can have a thickness up to 100 nm, but more typically less than10 nm (commonly referred to as few-layer graphene). Multiple graphenesheets or platelets may be made into a sheet of NGP paper (34) using apaper-making process.

Route 2 entails ultrasonicating the graphite oxide suspension for thepurpose of separating/isolating individual graphene oxide sheets fromgraphite oxide particles. This is based on the notion that theinter-graphene plane separation has been increased from 0.3354 nm innatural graphite to 0.6-1.1 nm in highly oxidized graphite oxide,significantly weakening the van der Waals forces that hold neighboringplanes together. Ultrasonic power can be sufficient to further separategraphene plane sheets to form separated, isolated, or discrete grapheneoxide (GO) sheets. These graphene oxide sheets can then be chemically orthermally reduced to obtain “reduced graphene oxides” (RGO) typicallyhaving an oxygen content of 0.001%-10% by weight, more typically0.01%-5% by weight, most typically and preferably less than 2% byweight.

For the purpose of defining the claims of the instant application, NGPsor graphene materials include discrete sheets/platelets of single-layerand multi-layer (typically less than 10 layers) pristine graphene,graphene oxide, reduced graphene oxide (RGO), graphene fluoride,graphene chloride, graphene bromide, graphene iodide, hydrogenatedgraphene, nitrogenated graphene, chemically functionalized graphene,doped graphene (e.g. doped by B or N). Pristine graphene has essentially0% oxygen. RGO typically has an oxygen content of 0.001%-5% by weight.Graphene oxide (including RGO) can have 0.001%-50% by weight of oxygen.Other than pristine graphene, all the graphene materials have 0.001%-50%by weight of non-carbon elements (e.g. O, H, N, B, F, Cl, Br, I, etc.).These materials are herein referred to as non-pristine graphenematerials.

All types of graphene sheets (along with particles of an anode orcathode active material) may be made into a paper form; e.g. using avacuum-assisted filtration procedure. All types of graphene sheets(along with particles of an anode or cathode active material) may bemade into a film form using a coating or casting procedure. Theseprocedures are well-known in the art.

A graphene foam may be prepared by using a procedure that includes ablowing agent. A blowing agent or foaming agent is a substance which iscapable of producing a cellular or foamed structure via a foamingprocess in a variety of materials that undergo hardening or phasetransition, such as polymers (plastics and rubbers), glass, and metals.They are typically applied when the material being foamed is in a liquidstate. It has not been previously known that a blowing agent can be usedto create a foamed material while in a solid state. More significantly,it has not been previously taught or hinted that an aggregate ofgraphene sheets can be converted into a graphene foam via a blowingagent. The cellular structure in a polymer matrix is typically createdfor the purpose of reducing density, increasing thermal resistance andacoustic insulation, while increasing the thickness and relativestiffness of the original polymer.

Blowing agents or related foaming mechanisms to create pores or cells(bubbles) in a matrix for producing a foamed or cellular material, canbe classified into the following groups:

-   (a) Physical blowing agents: e.g. hydrocarbons (e.g. pentane,    isopentane, cyclopentane), chlorofluorocarbons (CFCs),    hydrochlorofluorocarbons (HCFCs), and liquid CO₂. The    bubble/foam-producing process is endothermic, i.e. it needs heat    (e.g. from a melt process or the chemical exotherm due to    cross-linking), to volatize a liquid blowing agent.-   (b) Chemical blowing agents: e.g. isocyanate, azo-, hydrazine and    other nitrogen-based materials (for thermoplastic and elastomeric    foams), sodium bicarbonate (e.g. baking soda, used in thermoplastic    foams). Here gaseous products and other by-products are formed by a    chemical reaction, promoted by process or a reacting polymer's    exothermic heat. Since the blowing reaction involves forming low    molecular weight compounds that act as the blowing gas, additional    exothermic heat is also released. Powdered titanium hydride is used    as a foaming agent in the production of metal foams, as it    decomposes to form titanium and hydrogen gas at elevated    temperatures. Zirconium (II) hydride is used for the same purpose.    Once formed the low molecular weight compounds will never revert to    the original blowing agent(s), i.e. the reaction is irreversible.-   (c) Mixed physical/chemical blowing agents: e.g. used to produce    flexible polyurethane (PU) foams with very low densities. Both the    chemical and physical blowing can be used in tandem to balance each    other out with respect to thermal energy released/absorbed; hence,    minimizing temperature rise. For instance, isocyanate and water    (which react to form CO₂) are used in combination with liquid CO₂    (which boils to give gaseous form) in the production of very low    density flexible PU foams for mattresses.-   (d) Mechanically injected agents: Mechanically made foams involve    methods of introducing bubbles into liquid polymerizable matrices    (e.g. an unvulcanized elastomer in the form of a liquid latex).    Methods include whisking-in air or other gases or low boiling    volatile liquids in low viscosity lattices, or the injection of a    gas into an extruder barrel or a die, or into injection molding    barrels or nozzles and allowing the shear/mix action of the screw to    disperse the gas uniformly to form very fine bubbles or a solution    of gas in the melt. When the melt is molded or extruded and the part    is at atmospheric pressure, the gas comes out of solution expanding    the polymer melt immediately before solidification.-   (e) Soluble and leachable agents: Soluble fillers, e.g. solid sodium    chloride crystals mixed into a liquid urethane system, which is then    shaped into a solid polymer part, the sodium chloride is later    washed out by immersing the solid molded part in water for some    time, to leave small inter-connected holes in relatively high    density polymer products.-   (f) We have found that the above five mechanisms can all be used to    create pores in the graphene materials while they are in a solid    state. Another mechanism of producing pores in a graphene material    is through the generation and vaporization of volatile gases by    removing those non-carbon elements in a high-temperature    environment. This is a unique self-foaming process that has never    been previously taught or suggested.

In a preferred embodiment, the graphene material in the dispersion isselected from pristine graphene, graphene oxide, reduced graphene oxide,graphene fluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, chemically functionalizedgraphene, or a combination thereof. The starting graphitic material forproducing any one of the above graphene materials may be selected fromnatural graphite, artificial graphite, meso-phase carbon, meso-phasepitch, meso-carbon micro-bead, soft carbon, hard carbon, coke, carbonfiber, carbon nano-fiber, carbon nano-tube, or a combination thereof.

For instance, the graphene oxide (GO) may be obtained by immersingpowders or filaments of a starting graphitic material (e.g. naturalgraphite powder) in an oxidizing liquid medium (e.g. a mixture ofsulfuric acid, nitric acid, and potassium permanganate) in a reactionvessel at a desired temperature for a period of time (typically from 0.5to 96 hours, depending upon the nature of the starting material and thetype of oxidizing agent used). The resulting graphite oxide particlesmay then be subjected to thermal exfoliation or ultrasonic wave-inducedexfoliation to produce GO sheets.

Pristine graphene may be produced by direct ultrasonication (also knownas liquid phase production) or supercritical fluid exfoliation ofgraphite particles. These processes are well-known in the art. Multiplepristine graphene sheets may be dispersed in water or other liquidmedium with the assistance of a surfactant to form a suspension. Achemical blowing agent may then be dispersed into the dispersion (38 inFIG. 2). This suspension is then cast or coated onto the surface of asolid substrate (e.g. glass sheet or Al foil). When heated to a desiredtemperature, the chemical blowing agent is activated or decomposed togenerate volatile gases (e.g. N₂ or CO₂), which act to form bubbles orpores in an otherwise mass of solid graphene sheets, forming a pristinegraphene foam 40 a.

Fluorinated graphene or graphene fluoride is herein used as an exampleof the halogenated graphene material group. There are two differentapproaches that have been followed to produce fluorinated graphene: (1)fluorination of pre-synthesized graphene: This approach entails treatinggraphene prepared by mechanical exfoliation or by CVD growth withfluorinating agent such as XeF₂, or F-based plasmas; (2) Exfoliation ofmultilayered graphite fluorides: Both mechanical exfoliation and liquidphase exfoliation of graphite fluoride can be readily accomplished [F.Karlicky, et al. “Halogenated Graphenes: Rapidly Growing Family ofGraphene Derivatives” ACS Nano, 2013, 7 (8), pp 6434-6464].

Interaction of F₂ with graphite at high temperature leads to covalentgraphite fluorides (CF)_(n) or (C₂F)_(n), while at low temperaturesgraphite intercalation compounds (GIC) C_(x)F (2≤x≤24) form. In (CF)_(n)carbon atoms are sp3-hybridized and thus the fluorocarbon layers arecorrugated consisting of trans-linked cyclohexane chairs. In (C₂F)_(n)only half of the C atoms are fluorinated and every pair of the adjacentcarbon sheets are linked together by covalent C—C bonds. Systematicstudies on the fluorination reaction showed that the resulting F/C ratiois largely dependent on the fluorination temperature, the partialpressure of the fluorine in the fluorinating gas, and physicalcharacteristics of the graphite precursor, including the degree ofgraphitization, particle size, and specific surface area. In addition tofluorine (F₂), other fluorinating agents may be used, although most ofthe available literature involves fluorination with F₂ gas, sometimes inpresence of fluorides.

For exfoliating a layered precursor material to the state of individuallayers or few-layers, it is necessary to overcome the attractive forcesbetween adjacent layers and to further stabilize the layers. This may beachieved by either covalent modification of the graphene surface byfunctional groups or by non-covalent modification using specificsolvents, surfactants, polymers, or donor-acceptor aromatic molecules.The process of liquid phase exfoliation includes ultra-sonic treatmentof a graphite fluoride in a liquid medium.

The nitrogenation of graphene can be conducted by exposing a graphenematerial, such as graphene oxide, to ammonia at high temperatures(200-400° C.). Nitrogenated graphene could also be formed at lowertemperatures by a hydrothermal method; e.g. by sealing GO and ammonia inan autoclave and then increased the temperature to 150-250° C. Othermethods to synthesize nitrogen doped graphene include nitrogen plasmatreatment on graphene, arc-discharge between graphite electrodes in thepresence of ammonia, ammonolysis of graphene oxide under CVD conditions,and hydrothermal treatment of graphene oxide and urea at differenttemperatures.

The pore walls (cell walls or solid graphene portion) in the graphenefoam of the presently invented anode contain chemically bonded andmerged graphene planes. These planar aromatic molecules or grapheneplanes (hexagonal structured carbon atoms) are well interconnectedphysically and chemically. The lateral dimensions (length or width) ofthese planes are huge (e.g. from 20 nm to >10 μm), typically severaltimes or even orders of magnitude larger than the maximum crystallitedimension (or maximum constituent graphene plane dimension) of thestarting graphite particles. The graphene sheets or planes areessentially merged and/or interconnected to form electron-conductingpathways with low resistance. This is a unique and new class of materialthat has not been previously discovered, developed, or suggested topossibly exist.

In order to illustrate how the presently invented process works toproduce a layer of graphene foam-protected anode or cathode material, weherein make use of graphene oxide (GO) and graphene fluoride (GF) as twoexamples. These should not be construed as limiting the scope of ourclaims. In each case, the first step involves preparation of a graphenedispersion (e.g. GO+water or GF+organic solvent, DMF) containing anoptional blowing agent. If the graphene material is pristine graphenecontaining no non-carbon elements, a blowing agent is required.

In step (b), the GF or GO suspension (21 in FIG. 2), but now alsocontaining particles of an anode or cathode active material is formedinto a wet GF or GO layer 35 on a solid substrate surface (e.g. PET filmor glass) preferably under the influence of a shear stress. One exampleof such a shearing procedure is casting or coating a thin film of GF orGO suspension using a coating machine. This procedure is similar to alayer of varnish, paint, coating, or ink being coated onto a solidsubstrate. The roller or wiper creates a shear stress when the film isshaped, or when there is a high relative motion between theroller/blade/wiper and the supporting substrate. Quite unexpectedly andsignificantly, such a shearing action enables the planar GF or GO sheetsto well align along, for instance, a shearing direction. Furthersurprisingly, such a molecular alignment state or preferred orientationis not disrupted when the liquid components in the GF or GO suspensionare subsequently removed to form a well-packed layer of highly alignedGF or GO sheets that are at least partially dried. The dried GF or GOmass 37 a has a high birefringence coefficient between an in-planedirection and the normal-to-plane direction.

In an embodiment, this GF or GO layer, each containing Si particlestherein, is then subjected to a heat treatment to activate the blowingagent and/or the thermally-induced reactions that remove the non-carbonelements (e.g. F, 0, etc.) from the graphene sheets to generate volatilegases as by-products. These volatile gases generate pores or bubblesinside the solid graphene material, pushing solid graphene sheets into afoam wall structure, forming a graphene oxide foam (40 b in FIG. 2). Ifno blowing agent is added, the non-carbon elements in the graphenematerial preferably occupy at least 10% by weight of the graphenematerial (preferably at least 20%, and further preferably at least 30%).The first (initial) heat treatment temperature is typically greater than80° C., preferably greater than 100° C., more preferably greater than300° C., further more preferably greater than 500° C. and can be as highas 1,500° C. The blowing agent is typically activated at a temperaturefrom 80° C. to 300° C., but can be higher. The foaming procedure(formation of pores, cells, or bubbles) is typically completed withinthe temperature range of 80-1,500° C. Quite surprisingly, the chemicallinking or merging between graphene planes (GO or GF planes) in anedge-to-edge and face-to-face manner can occur at a relatively low heattreatment temperature (e.g. even as low as from 150 to 300° C.).

The foamed graphene material may be subjected to a further heattreatment that involves at least a second temperature that issignificantly higher than the first heat treatment temperature.

A properly programmed heat treatment procedure can involve just a singleheat treatment temperature (e.g. a first heat treatment temperatureonly), at least two heat treatment temperatures (first temperature for aperiod of time and then raised to a second temperature and maintained atthis second temperature for another period of time), or any othercombination of heat treatment temperatures (HTT) that involve an initialtreatment temperature (first temperature) and a final HTT (second),higher than the first. The highest or final HTT that the dried graphenelayer experiences may be divided into three distinct HTT regimes:

-   Regime 1 (80° C. to 300° C.): In this temperature range (the thermal    reduction regime and also the activation regime for a blowing agent,    if present), a GO or GF layer primarily undergoes thermally-induced    reduction reactions, leading to a reduction of oxygen content or    fluorine content from typically 20-50% (of O in GO) or 10-25% (of F    in GF) to approximately 5-6%. This treatment results in a reduction    of inter-graphene spacing in foam walls from approximately 0.6-1.2    nm (as dried) down to approximately 0.4 nm, and an increase in    thermal conductivity to 200 W/mK per unit specific gravity and/or    electrical conductivity to 2,000 S/cm per unit of specific gravity.    (Since one can vary the level of porosity and, hence, specific    gravity of a graphene foam material and, given the same graphene    material, both the thermal conductivity and electric conductivity    values vary with the specific gravity, these property values must be    divided by the specific gravity to facilitate a fair comparison.)    Even with such a low temperature range, some chemical linking    between graphene sheets occurs. The inter-GO or inter-GF planar    spacing remains relatively large (0.4 nm or larger). Many O- or    F-containing functional groups survive.-   Regime 2 (300° C.-1,500° C.): An important event occurs in this    temperature range: The event relates to the formation of the    graphene foam structure. In this chemical linking regime, extensive    chemical combination, polymerization, and cross-linking between    adjacent GO or GF sheets occur. The oxygen or fluorine content is    reduced to typically <1.0% (e.g. 0.7%) after chemical linking,    resulting in a reduction of inter-graphene spacing to approximately    0.345 nm. This implies that some initial re-graphitization has    already begun at such a low temperature, in stark contrast to    conventional graphitizable materials (such as carbonized polyimide    film) that typically require a temperature as high as 2,500° C. to    initiate graphitization. This is another distinct feature of the    presently invented graphene foam and its production processes. These    chemical linking reactions result in an increase in thermal    conductivity to 250 W/mK per unit of specific gravity, and/or    electrical conductivity to 2,500-4,000 S/cm per unit of specific    gravity.-   Regime 3 (1,500-2,500° C.): In this ordering and re-graphitization    regime, extensive graphitization or graphene plane merging occurs,    leading to significantly improved degree of structural ordering in    the foam walls. As a result, the oxygen or fluorine content is    reduced to typically 0.01% and the inter-graphene spacing to    approximately 0.337 nm (achieving degree of graphitization from 1%    to approximately 80%, depending upon the actual HTT and length of    time). The improved degree of ordering is also reflected by an    increase in thermal conductivity to >350 W/mK per unit of specific    gravity, and/or electrical conductivity to >3,500 S/cm per unit of    specific gravity.-   Regime 4 (>2,500° C.): Re-graphitization or re-crystallization.

The presently invented graphene foam structure containing an anode orcathode active material therein can be obtained by heat-treating thedried GO or GF layer with a temperature program that covers at least thefirst regime (typically requiring 1-4 hours in this temperature range ifthe temperature never exceeds 500° C.), more commonly covers the firsttwo regimes (1-2 hours preferred), still more commonly the first threeregimes (preferably 0.5-2.0 hours in Regime 3), and can cover all the 4regimes (including Regime 4 for 0.2 to 1 hour, may be implemented toachieve the highest conductivity).

If the graphene material is selected from the group of non-pristinegraphene materials consisting of graphene oxide, reduced graphene oxide,graphene fluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, chemically functionalizedgraphene, or a combination thereof, and wherein the maximum heattreatment temperature (e.g. both the first and second heat treatmenttemperatures) is (are) less than 2,500° C., then the resulting solidgraphene foam typically contains a content of non-carbon elements in therange of 0.01% to 2.0% by weight (non-pristine graphene foam).

X-ray diffraction patterns were obtained with an X-ray diffractometerequipped with CuKcv radiation. The shift and broadening of diffractionpeaks were calibrated using a silicon powder standard. The degree ofgraphitization, g, was calculated from the X-ray pattern using theMering's Eq, d₀₀₂=0.3354 g+0.344 (l-g), where d₀₀₂ is the interlayerspacing of graphite or graphene crystal in nm. This equation is validonly when d₀₀₂ is equal or less than approximately 0.3440 nm. Thegraphene foam walls having a d₀₀₂ higher than 0.3440 nm reflects thepresence of oxygen- or fluorine-containing functional groups (such as—F, —OH, >O, and —COOH on graphene molecular plane surfaces or edges)that act as a spacer to increase the inter-graphene spacing.

Another structural index that can be used to characterize the degree ofordering of the stacked and bonded graphene planes in the foam walls ofgraphene and conventional graphite crystals is the “mosaic spread,”which is expressed by the full width at half maximum of a rocking curve(X-ray diffraction intensity) of the (002) or (004) reflection. Thisdegree of ordering characterizes the graphite or graphene crystal size(or grain size), amounts of grain boundaries and other defects, and thedegree of preferred grain orientation. A nearly perfect single crystalof graphite is characterized by having a mosaic spread value of 0.2-0.4.Most of our graphene walls have a mosaic spread value in this range of0.2-0.4 (if produced with a heat treatment temperature (HTT) no lessthan 2,500° C.). However, some values are in the range of 0.4-0.7 if theHTT is between 1,500 and 2,500° C., and in the range of 0.7-1.0 if theHTT is between 300 and 1,500° C.

Illustrated in FIG. 4 is a plausible chemical linking mechanism whereonly 2 aligned GO molecules are shown as an example, although a largenumber of GO molecules can be chemically linked together to form a foamwall. Further, chemical linking could also occur face-to-face, not justedge-to-edge for GO, GF, and chemically functionalized graphene sheets.These linking and merging reactions proceed in such a manner that themolecules are chemically merged, linked, and integrated into one singleentity. The graphene sheets (GO or GF sheets) completely lose their ownoriginal identity and they no longer are discretesheets/platelets/flakes.

The resulting product is not a simple aggregate of individual graphenesheets, but a single entity that is essentially a network ofinterconnected giant molecules with an essentially infinite molecularweight. This may also be described as a graphene poly-crystal (withseveral grains, but typically no discernible, well-defined grainboundaries). All the constituent graphene planes are very large inlateral dimensions (length and width) and, if the HTT is sufficientlyhigh (e.g. >1,500° C. or much higher), these graphene planes areessentially bonded together with one another. The graphene foam of thepresently invented anode layer or cathode layer has the following uniqueand novel features that have never been previously taught or hinted.These features make these electrode layers (having active materialsembedded therein) function as current collectors as well, obviating theneed to have a separate current collector in the anode or cathode:

-   (1) In-depth studies using a combination of SEM, TEM, selected area    diffraction, X-ray diffraction, AFM, Raman spectroscopy, and FTIR    indicate that the graphene foam walls are composed of several huge    graphene planes (with length/width typically >>20 nm, more    typically >>100 nm, often >>1 μm, and, in many cases, >>10 μm, or    even >>100 μm). These giant graphene planes are stacked and bonded    along the thickness direction (crystallographic c-axis direction)    often through not just the van der Waals forces (as in conventional    graphite crystallites), but also covalent bonds, if the final heat    treatment temperature is lower than 2,500° C. In these cases,    wishing not to be limited by theory, but Raman and FTIR spectroscopy    studies appear to indicate the co-existence of sp² (dominating) and    sp³ (weak but existing) electronic configurations, not just the    conventional sp² in graphene planes.-   (2) These interconnected large graphene planes in the graphene foam    walls form an integral 3D network of graphene that is not only    highly conducting but also elastic, enabling the foam pores to    expand and shrink reversibly and in congruent with anode active    material particles lodged in the pores without inducing significant    anode electrode expansion or shrinkage in the battery.-   (3) This graphene foam wall is not made by gluing or bonding    discrete flakes/platelets together with a resin binder, linker, or    adhesive. Instead, GO sheets (molecules) from the GO dispersion or    the GF sheets from the GF dispersion are merged through joining or    forming of covalent bonds with one another, into an integrated    graphene entity, without using any externally added linker or binder    molecules or polymers. For a lithium battery featuring such an anode    layer, there is no need to have non-active materials, such as a    resin binder or a conductive additive, which are incapable of    storing lithium. This implies a reduced amount of non-active    materials or increased amount of active materials in the anode,    effectively increasing the specific capacity per total anode weight,    mAh/g (of composite).-   (4) The graphene foam pore walls are typically a poly-crystal    composed of large graphene grains having incomplete or poorly    defined grain boundaries. This entity is derived from a GO or GF    suspension, which is in turn obtained from natural graphite or    artificial graphite particles originally having multiple graphite    crystallites. Prior to being chemically oxidized or fluorinated,    these starting graphite crystallites have an initial length (L_(a)    in the crystallographic a-axis direction), initial width (L_(b) in    the b-axis direction), and thickness (L_(c) in the c-axis    direction). Upon oxidation or fluorination, these initially discrete    graphite particles are chemically transformed into highly aromatic    graphene oxide or graphene fluoride molecules having a significant    concentration of edge- or surface-borne functional groups (e.g. —F,    —OH, —COOH, etc.). These aromatic GO or GF molecules in the    suspension have lost their original identity of being part of a    graphite particle or flake. Upon removal of the liquid component    from the suspension, the resulting GO or GF molecules form an    essentially amorphous structure. Upon heat treatments, these GO or    GF molecules are chemically merged and linked into a unitary or    monolithic graphene entity that constitutes the foam wall. This foam    wall is highly ordered.

The resulting unitary graphene entity in the foam wall typically has alength or width significantly greater than the L_(a) and L_(b) of theoriginal crystallites. The length/width of this graphene foam wallentity is significantly greater than the L_(a) and L_(b) of the originalcrystallites. Even the individual grains in a poly-crystalline graphenewall structure have a length or width significantly greater than theL_(a) and L_(b) of the original crystallites.

-   (5) The large length and width of the graphene planes enable the    foam walls to be of high mechanical strength and elasticity. In    comparative experiments, we observe that without this feature (i.e.    no chemical merging of graphene planes), conventionally made    graphene foams composed of aggregates of discrete graphene sheets,    are relatively weak, fragile, and non-elastic (deformation not    reversible).-   (6) Due to these unique chemical composition (including oxygen or    fluorine content), morphology, crystal structure (including    inter-graphene spacing), and structural features (e.g. high degree    of orientations, few defects, incomplete grain boundaries, chemical    bonding and no gap between graphene sheets, and substantially no    interruptions in graphene planes), the GO- or GF-derived graphene    foam has a unique combination of outstanding thermal conductivity,    electrical conductivity, mechanical strength, and stiffness (elastic    modulus).

The following examples are used to illustrate some specific detailsabout the best modes of practicing the instant invention and should notbe construed as limiting the scope of the invention.

Example 1: Evaluation of Various Battery Cells

For electrochemical testing, several types of anodes and cathodes wereprepared. For instance, a layer-type of anode or cathode was prepared bysimply roll-pressing the foam (including an anode or cathode activematerial embedded therein) against a sheet of Cu foil (as an anodecurrent collector). Some foam samples containing an anode activematerial were used as an anode electrode without using a separate Cufoil current collector. Some foam samples containing a cathode activematerial were used as a cathode electrode without using a separate Alfoil current collector.

For comparison purposes, slurry coating was also used to prepareconventional electrodes. For instance, the working electrodes wereprepared by mixing 85 wt. % active material (SnO₂ particles, 7 wt. %acetylene black (Super-P), and 8 wt. % polyvinylidene fluoride (PVDF, 5wt. % solid content) binder dissolved in N-methyl-2-pyrrolidinoe (NMP).After coating the slurries on Cu foil, the electrodes were dried at 120°C. in vacuum for 2 h to remove the solvent before pressing.

Then, the electrodes were cut into a disk (ϕ=12 mm) and dried at 100° C.for 24 h in vacuum. Electrochemical measurements were carried out usingCR2032 (3V) coin-type cells with lithium metal (as one example) as thecounter/reference electrode, Celgard 2400 membrane as separator, and (asan example of electrolyte) 1 M LiPF₆ electrolyte solution dissolved in amixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC-DEC,1:1 v/v). Various anode and cathode material compositions wereevaluated. The cell assembly was performed in an argon-filled glove-box.The CV measurements were carried out using an electrochemicalworkstation at a scanning rate of 1-100 mV/s. The electrochemicalperformance of various cells was also evaluated by galvanostaticcharge/discharge cycling at a current density of 50-1,000 mA/g, using aLAND electrochemical workstation. Full-cell pouch were also prepared andtested.

The following examples of low-voltage cells can be (and have been in ourlab) connected to sensors, small actuators, small hearing aids (anexample of small medical devices), small wireless circuits, wearabledevices, etc.

Example 2: Low-Voltage Al—S Cells (Aqueous or Organic Electrolytes)

From the electrochemical reaction perspective, sulfur (S) is a bivalentmaterial that can accept/give two electrons during redox reactions. Theactual capacity is around 1,980 mAh/cm³. If paired with an aluminumanode, the output voltage is found to be ˜0.73 V (FIG. 5). The voltagevariation between 10% DoD and 90% DoD is ±2.1%.

Anode reaction: Al+7AlCl₄ ⁻→4Al₂Cl₇ ⁻+3e ⁻

Cathode reaction: M₁+2e ⁻→M₁ ²⁻(M₁=S)

Full reaction: 2Al³⁺+6e ⁻+3M₁→Al₂(M₁)₃

Example 3: Low-Voltage Li—P Cells

M₂ (M₂=P) is a trivalent material that can accept/give three electronsduring redox reactions. The actual capacity is around 2,371 mAh/cm³ at100% DoD (FIG. 6). When paired with a lithium anode, it gave the outputvoltage of −0.32 V. The voltage variation between 10% DoD and 90% DoD is±14%. With the presence of 20% by weight graphene in the cathode, thedischarge curve is shifted upward by a full 0.1 volts and the slope issignificantly decreased (more stable voltage output). These unexpectedimprovements are highly beneficial.

Anode reaction: Li→Li⁺ +e ⁻

Cathode reaction: M₂+3e ⁻→M₂ ³⁻

Full reaction: 3Li⁺+3e ⁻+M₂→Li₃(M₂)

Example 4: Low-Voltage Li—SnO₂ Cells

M₄ (compound A_(y)B_(z)=SnO₂) is a multivalent material that canaccept/give multi electrons during redox reactions. The discharge curveconsists of two regions, a level plateau and a slope curve (FIG. 7). Theactual capacity of the slope curve is around 6,157 mAh/cm³ at 100% DoD.When paired with a lithium anode and only the slope region is utilized,it gave the output voltage of −0.35 V. The voltage variation between 10%DoD and 90% DoD is ±68%. However, one can identify a Vf wherein thevoltage variation, (Vi−Vf)/Vi, is no greater than ±10% since thespecific capacity is so large.

Anode reaction: Li→Li⁺ +e ⁻

Cathode reaction: A(M₄)+xe ⁻→A(M₄)^(x−)

Full reaction: xLi⁺ +xe ⁻+A(M₄)→Li_(x)(A(M₄))

Example 5: Low-Voltage Na—SnO₂ Cells

M₄ (compound A_(y)B_(z)=SnO₂) is a multivalent material that canaccept/give multi electrons during redox reactions. The discharge curveconsists of two regions, a level plateau and a slope curve (FIG. 8). Theactual capacity is around 3,315 mAh/cm³ at 100% DoD. When paired with asodium anode and only the plateau region is utilized, it gave the outputvoltage of −0.55 V. The voltage variation between 10% DoD and 90% DoD is±5%.

Anode reaction: Na→Na⁺ +e ⁻

Cathode reaction: A_(y)B_(z)(M₄)+xe ⁻ →yA(M₄)+zB(M₄)^((x/z)−)

Full reaction: xNa⁺ +xe ⁻+A_(y)B_(z)(M₄)→yA(M₄)+zNa_((x/z))B(M₄)

Example 6: Low-Voltage Li—Sb Cells

M₇ (Sb) is a multivalent material that can accept/give multi electronsduring redox reactions. The actual capacity is around 3,355 mAh/cm³.When paired with a lithium anode, it gave the output voltage of −0.80 V(FIG. 9). The voltage variation between 10% DoD and 90% DoD is ±2.4%.

Anode reaction: Li→Li⁺ +e ⁻

Cathode reaction: M₇ +xe ⁻→M₇ ^(x−)

Full reaction: xLi⁺ +xe ⁻+M₇→Li_(x)(M₇)

Example 7: Low-Voltage Na—Sb Cells

M₇ (Sb) is a multivalent material that can accept/give multi electronsduring redox reactions. The actual capacity is around 3,355 mAh/cm³.When paired with a sodium anode, it gave the output voltage of −0.47 V(FIG. 10). The voltage variation between 10% DoD and 90% DoD is ±2.4%.

Anode reaction: Na→Na⁺ +e ⁻

Cathode reaction: M₇ +xe ⁻→M₇ ^(x−)

Full reaction: xNa⁺ +xe ⁻+M₇→Na_(x)(M₇)

Example 8: Low-Voltage Li—Fe₃O₄ Cells

M₈ (compound A_(y)B_(z)=Fe₃O₄) is a multivalent material that canaccept/give multi electrons during redox reactions. The actual capacityis around 3,650 mAh/cm³. When paired with a lithium anode, it gave theoutput voltage of −0.83 V (FIG. 11). The voltage variation between 10%DoD and 90% DoD is ±3.3%.

Anode reaction: Li→Li⁺ +e ⁻

Cathode reaction: A_(y)B_(z)(M₈)+xe ⁻ →yA(M₈)+zB(M₈)^((x/z)−)

Full reaction: xLi⁺ +xe ⁻+A_(y)B_(z)(M₈)→yA(M₈)+zLi_((x/z))B(M₈)

Example 9: Low-Voltage Na—Fe₃O₄ Cells

M₈ (compound A_(y)B_(z)=Fe₃O₄) is a multivalent material that canaccept/give multi electrons during redox reactions. The actual capacityis around 3,650 mAh/cm³. When paired with a sodium anode, it gave theoutput voltage of −0.5 V (FIG. 12). The voltage variation between 10%DoD and 90% DoD is ±3.3%.

Anode reaction: Na→Na⁺ +e ⁻

Cathode reaction: A_(y)B_(z)(M₈)+xe ⁻ →yA(M₈)+zB(M₈)^((x/z)−)

Full reaction: xNa⁺ +xe ⁻+A_(y)B_(z)(M₈)→yA(M₈)+zNa_((x/z))B(M₈)

Example 10: Low-Voltage Li—Sn Cells

M₉ (Sn) is a multivalent material that can accept/give multi electronsduring redox reactions. The actual capacity is around 5,818 mAh/cm³.When paired with a lithium anode, it gave the output voltage of −0.42 V(FIG. 13). The voltage variation between 10% DoD and 90% DoD is ±48%.

Anode reaction: Li→Li⁺ +e ⁻

Cathode reaction: M₉ +xe ⁻→M₉ ^(x−)

Full reaction: xLi⁺ +xe ⁻+M₉→Li_(x)(M₉)

Example 10: Low-Voltage Li—Mn₃O₄ and Graphene-Modified Li—Mn₃O₄ Cells

M₁₀ (compound A_(y)B_(z)=Mn₃O₄) is a multivalent material that canaccept/give multi electrons during redox reactions. The actual capacityis around 3,615 mAh/cm³. When paired with a lithium anode, it gave theoutput voltage of −0.32 V (FIG. 14). The voltage variation between 10%DoD and 90% DoD is ±6.5%. With the cathode active material (nanoparticles of Mn₃O₄) being bonded to nitrogenated graphene sheets, thecell output voltage is shifted up to a more useful range and the slopeis also reduced (a better plateau of curve).

Anode reaction: Li→Li⁺ +e ⁻

Cathode reaction: A_(y)B_(z)(M₁₀)+xe ⁻ →yA(M₁₀)+zB(M₁₀)^((x/z)−)

Full reaction: xLi⁺ +xe ⁻+A_(y)B_(z)(M₁₀)→yA(M₁₀)+zLi_((X/z))B(M₁₀)

Example 11: Low-Voltage Li—Al Cells

M₁₁(Al) is a multivalent material that can accept/give multi electronsduring redox reactions. The actual capacity is around 2,748 mAh/cm³.When paired with a lithium anode, it gave the output voltage of −0.30 V(FIG. 15). The voltage variation between 10% DoD and 90% DoD is ±1.8%.

Anode reaction: Li→Li⁺ +e ⁻

Cathode reaction: M₁₁ +xe ⁻→M₁₁ ^(x−)

Full reaction: xLi⁺ +xe ⁻+M₁₁→Li_(x)(M₁₁)

Example 12: Low-Voltage Li—MoO₃ Cells

M₁₂ (compound A_(y)B_(z)=MoO₃) is a multivalent material that canaccept/give multi electrons during redox reactions. The actual capacityis around 3,503 mAh/cm³. When paired with a lithium anode, it gave theoutput voltage of −0.41 V (FIG. 16). The voltage variation between 10%DoD and 90% DoD is ±14%.

Anode reaction: Li→Li⁺ +e ⁻

Cathode reaction: A_(y)B_(z)(M₁₂)+xe ⁻ →yA(M₁₂)+zB(M₁₂)^((x/z)−)

Full reaction: xLi⁺ +xe ⁻+A_(y)B_(z)(M₁₂)→yA(M₁₂)+zLi_((x/z))B(M₁₂)

Example 13: Low-Voltage Li—MoS₂ Cells

M₁₃ (compound A_(y)B_(z)=MoS₂) is a multivalent material that canaccept/give multi electrons during redox reactions. The actual capacityis around 2,509 mAh/cm³. When paired with a lithium anode, it gave theoutput voltage of −0.58 V (FIG. 17). The voltage variation between 10%DoD and 90% DoD is ±6.4%.

Anode reaction: Li→Li⁺ +e ⁻

Cathode reaction: A_(y)B_(z)(M₁₃)+xe ⁻ →yA(M₁₃)+zB(M₁₃)^((x/z)−)

Full reaction: xLi⁺ +xe ⁻+A_(y)B_(z)(M₁₃)→yA(M₁₃)+zLi_((x/z))B(M₁₃)

Example 14: Preparation of discrete functionalized GO sheets andgraphene foam

Chopped graphite fibers with an average diameter of 12 μm and naturalgraphite particles were separately used as a starting material, whichwas immersed in a mixture of concentrated sulfuric acid, nitric acid,and potassium permanganate (as the chemical intercalate and oxidizer) toprepare graphite intercalation compounds (GICs). The starting materialwas first dried in a vacuum oven for 24 h at 80° C. Then, a mixture ofconcentrated sulfuric acid, fuming nitric acid, and potassiumpermanganate (at a weight ratio of 4:1:0.05) was slowly added, underappropriate cooling and stirring, to a three-neck flask containing fibersegments. After 5-16 hours of reaction, the acid-treated graphite fibersor natural graphite particles were filtered and washed thoroughly withdeionized water until the pH level of the solution reached 5. After adrying treatment at 100° C. overnight, the resulting graphiteintercalation compound (GIC) or graphite oxide fiber was re-dispersed inwater-alcohol to form a slurry.

In one sample, five grams of the graphite oxide fibers were mixed with2,000 ml alcohol solution consisting of alcohol and distilled water witha ratio of 15:85 to obtain a slurry mass. Then, the mixture slurry wassubjected to ultrasonic irradiation with a power of 200 W for variouslengths of time. After 20 minutes of sonication, GO fibers wereeffectively exfoliated and separated into thin graphene oxide sheetswith oxygen content of approximately 23%-31% by weight. Ammonia waterwas added to one pot of the resulting suspension, which wasultrasonicated for another hour to produce NH₂-functionalized grapheneoxide (f-GO). The GO sheets and functionalized GO sheets were separatelydiluted to a weight fraction of 5% and a desired amount of SnO₂particles (as an example of cathode active material in a low-voltagecell) was added to the suspensions. Subsequently, 2% baking soda as ablowing agent, was added to the GO/SnO₂ or f-GO/SnO₂ suspensions to formmixture slurries. The resulting slurries were allowed to stay in thecontainer without any mechanical disturbance for 2 days.

The resulting slurries containing GO/SnO₂ or f-GO/SnO₂ were thencomma-coated onto a PET film surface. The resulting coating films, afterremoval of liquid, have a thickness that was from 100 to 800 μm. Thefilms were then subjected to heat treatments that involve an initialheat treatment temperature of 500° C. for 2 hours (in a mixture of H₂and N₂) to enable formation of a foamed structure. This is followed byexposing the foam at a second temperature of 800-1,200° C. (in Ar gasatmosphere) for different specimens.

Example 15: Preparation of Single-Layer Graphene Sheets from Meso-CarbonMicro-Beads (MCMBs) and Graphene Foam

Meso-carbon microbeads (MCMBs) were supplied from China Steel ChemicalCo., Kaohsiung, Taiwan. This material has a density of about 2.24 g/cm³with a median particle size of about 16 μm. MCMB (10 grams) wereintercalated with an acid solution (sulfuric acid, nitric acid, andpotassium permanganate at a ratio of 4:1:0.05) for 48-96 hours. Uponcompletion of the reaction, the mixture was poured into deionized waterand filtered. The intercalated MCMBs were repeatedly washed in a 5%solution of HCl to remove most of the sulphate ions. The sample was thenwashed repeatedly with deionized water until the pH of the filtrate wasno less than 4.5. The slurry was then subjected ultrasonication for10-100 minutes to produce GO suspensions. TEM and atomic forcemicroscopic studies indicate that most of the GO sheets weresingle-layer graphene when the oxidation treatment exceeded 72 hours,and 2- or 3-layer graphene when the oxidation time was from 48 to 72hours.

The GO sheets contain oxygen proportion of approximately 35%-47% byweight for oxidation treatment times of 48-96 hours. GO sheets weresuspended in water. MoO₃ particles having diameter of 1-6 μm (anotherexample of cathode active material) were added to the GO suspension.Baking soda (5-20% by weight), as a chemical blowing agent, was alsoadded to the suspension just prior to casting. The suspension was thencast onto a glass surface using a doctor's blade to exert shearstresses, inducing GO sheet orientations. Several samples were cast,some containing a blowing agent and some not. The resulting GO films,after removal of liquid, have a thickness that can be varied fromapproximately 10 to 500 μm.

The several sheets of the GO film, with or without a blowing agent, werethen subjected to heat treatments that involve an initial (first)thermal reduction temperature of 80-500° C. for 1-5 hours. This firstheat treatment generated a graphene foam. The foam was then subjected toa second temperature of 750-950° C. for 4 hours.

Example 16: Preparation of Pristine Graphene Film and Foam (0% Oxygen)

Recognizing the high defect population in GO sheets acting to reduce theconductivity of individual graphene plane, we decided to study if theuse of pristine graphene sheets (non-oxidized and oxygen-free,non-halogenated and halogen-free, etc.) can lead to a graphene foamhaving a higher thermal conductivity. Pristine graphene sheets wereproduced by using the direct ultrasonication or liquid-phase productionprocess.

In a typical procedure, five grams of graphite flakes, ground toapproximately 20 μm or less in sizes, were dispersed in 1,000 mL ofdeionized water (containing 0.1% by weight of a dispersing agent, Zonyl®FSO from DuPont) to obtain a suspension. An ultrasonic energy level of85 W (Branson 5450 Ultrasonicator) was used for exfoliation, separation,and size reduction of graphene sheets for a period of 15 minutes to 2hours. The resulting graphene sheets are pristine graphene that havenever been oxidized and are oxygen-free and relatively defect-free.There are essentially no other non-carbon elements.

Various amounts (0%-30% by weight relative to graphene material) ofchemical bowing agents (N, N-Dinitroso pentamethylene tetramine or 4.4′-Oxybis (benzenesulfonyl hydrazide) and MoS₂ particles (as an exampleof cathode active material) were added to a suspension containingpristine graphene sheets and a surfactant. The suspension was then slotdie-coated onto a PET film surface, which involves shear stress-inducedorientation of graphene sheets. The resulting graphene-Si films, afterremoval of liquid, have a thickness from approximately 100 to 750 μm.

The graphene films were then subjected to heat treatments that involvean initial (first) temperature of 80-1,500° C. for 1-5 hours, which ledto the production of a graphene film (if 0% blowing agent) or foam layer(with some blowing agent). Some of the pristine foam samples were thensubjected to a heat treatment at a second temperature of 700-2,500° C.

Example 17: Preparation of Graphene Oxide (GO) Suspension from NaturalGraphite and Subsequent Preparation of GO Foams

Graphite oxide was prepared by oxidation of graphite flakes with anoxidizer liquid consisting of sulfuric acid, sodium nitrate, andpotassium permanganate at a ratio of 4:1:0.05 at 30° C. When naturalgraphite flakes (particle sizes of 14 μm) were immersed and dispersed inthe oxidizer mixture liquid for 48 hours, the suspension or slurryappears and remains optically opaque and dark. After 48 hours, thereacting mass was rinsed with water 3 times to adjust the pH value to atleast 3.0. A final amount of water was then added to prepare a series ofGO-water suspensions. We observed that GO sheets form a liquid crystalphase when GO sheets occupy a weight fraction >3% and typically from 5%to 15%.

By dispensing and coating the GO suspension (containing particles of ananode or cathode active material) on a polyethylene terephthalate (PET)film in a slurry coater and removing the liquid medium from the coatedfilm we obtained a thin film of dried graphene oxide. Several GO filmsamples were then subjected to different heat treatments, whichtypically include a thermal reduction treatment at a first temperatureof 100° C. to 500° C. for 1-10 hours, and at a second temperature of750-1,500° C. for 0.5-5 hours, followed by a controlled cool-downprocedure. With these heat treatments, also under a compressive stress,the GO films were transformed into graphene foam.

On a separate basis, a certain amount of hydrazine, as a chemicalreducing agent, was added to the GO suspension (containing activematerial particles) to obtain reduced GO (RGO) suspension. The RGOsuspension was then subjected to a well-known vacuum-assisted filtrationprocedure to form RGO paper.

Example 18: Preparation of Graphene Foams (Containing Particles of anAnode or Cathode Active Material) from Graphene Fluoride

Several processes have been used by us to produce GF, but only oneprocess is herein described as an example. In a typical procedure,highly exfoliated graphite (HEG) was prepared from intercalated compoundC₂F.xClF₃. HEG was further fluorinated by vapors of chlorine trifluorideto yield fluorinated highly exfoliated graphite (FHEG). Pre-cooledTeflon reactor was filled with 20-30 mL of liquid pre-cooled ClF₃, thereactor was closed and cooled to liquid nitrogen temperature. Then, nomore than 1 g of HEG was put in a container with holes for ClF₃ gas toaccess and situated inside the reactor. In 7-10 days a gray-beigeproduct with approximate formula C₂F was formed.

Subsequently, a small amount of FHEG (approximately 0.5 mg) was mixedwith 20-30 mL of an organic solvent (methanol, ethanol, 1-propanol,2-propanol, 1-butanol, tert-butanol, isoamyl alcohol) and subjected toan ultrasound treatment (280 W) for 30 min, leading to the formation ofhomogeneous yellowish dispersions. Five minutes of sonication was enoughto obtain a relatively homogenous dispersion, but longer sonicationtimes ensured better stability. Particles of an anode or cathode activematerial were then added to the dispersion. Upon casting on a glasssurface with the solvent removed, the dispersion became a brownish filmformed on the glass surface. When GF films were heat-treated, fluorinewas released as gases that helped to generate pores in the film. In somesamples, a physical blowing agent (N₂ gas) was injected into the wet GFfilm while being cast. These samples exhibit much higher pore volumes orlower foam densities. Without using a blowing agent, the resultinggraphene fluoride foams exhibit physical densities from 0.35 to 1.38g/cm³. When a blowing agent was used (blowing agent/GF weight ratio from0.5/1 to 0.05/1), a density from 0.02 to 0.35 g/cm³ was obtained.Typical fluorine contents are from 0.001% (HTT=2,500° C.) to 4.7%(HTT=350° C.), depending upon the final heat treatment temperatureinvolved.

Example 19: Preparation of Graphene Foams (Containing Particles of anAnode or Cathode Active Material) from Nitrogenated Graphene

Graphene oxide (GO), synthesized in Example 2, was finely ground withdifferent proportions of urea and the pelletized mixture heated in amicrowave reactor (900 W) for 30 s. The product was washed several timeswith deionized water and vacuum dried. In this method graphene oxidegets simultaneously reduced and doped with nitrogen. The productsobtained with graphene:urea mass ratios of 1:0.5, 1:1 and 1:2 aredesignated as NGO-1, NGO-2 and NGO-3 respectively and the nitrogencontents of these samples were 14.7, 18.2 and 17.5 wt % respectively asfound by elemental analysis. These nitrogenataed graphene sheets remaindispersible in water. Particles of an anode or cathode active materialwere then added to the dispersion. The resulting suspensions were thencast, dried, and heat-treated initially at 200-350° C. as a first heattreatment temperature and subsequently treated at a second temperatureof 1,500° C. The resulting nitrogenated graphene foams exhibit physicaldensities from 0.45 to 1.28 g/cm³. Typical nitrogen contents of thefoams are from 0.01% (HTT=1,500° C.) to 5.3% (HTT=350° C.), dependingupon the final heat treatment temperature involved.

Example 20: Characterization of Various Graphene Foams and ConventionalGraphite Foam

The internal structures (crystal structure and orientation) of severaldried GO layers, and the heat-treated films at different stages of heattreatments were investigated using X-ray diffraction. The X-raydiffraction curve of natural graphite typically exhibits a peak atapproximately 20=26°, corresponds to an inter-graphene spacing (d₀₀₂) ofapproximately 0.3345 nm. Upon oxidation, the resulting GO shows an X-raydiffraction peak at approximately 20=12°, which corresponds to aninter-graphene spacing (d₀₀₂) of approximately 0.7 nm. With some heattreatment at 150° C., the dried GO compact exhibits the formation of ahump centered at 22°, indicating that it has begun the process ofdecreasing the inter-graphene spacing due to the beginning of chemicallinking and ordering processes. With a heat treatment temperature of2,500° C. for one hour, the d₀₀₂ spacing has decreased to approximately0.336, close to 0.3354 nm of a graphite single crystal.

With a heat treatment temperature of 2,750° C. for one hour, the d₀₀₂spacing is decreased to approximately to 0.3354 nm, identical to that ofa graphite single crystal. In addition, a second diffraction peak with ahigh intensity appears at 20=55° corresponding to X-ray diffraction from(004) plane. The (004) peak intensity relative to the (002) intensity onthe same diffraction curve, or the I(004)/I(002) ratio, is a goodindication of the degree of crystal perfection and preferred orientationof graphene planes. The (004) peak is either non-existing or relativelyweak, with the I(004)/I(002) ratio<0.1, for all graphitic materials heattreated at a temperature lower than 2,800° C. The I(004)/I(002) ratiofor the graphitic materials heat treated at 3,000-3,250° C. (e.g. highlyoriented pyrolytic graphite, HOPG) is in the range of 0.2-0.5. Incontrast, a graphene foam prepared with a final HTT of 2,750° C. for onehour exhibits a I(004)/I(002) ratio of 0.78 and a Mosaic spread value of0.21, indicating a practically perfect graphene single crystal with agood degree of preferred orientation.

The “mosaic spread” value is obtained from the full width at halfmaximum of the (002) reflection in an X-ray diffraction intensity curve.This index for the degree of ordering characterizes the graphite orgraphene crystal size (or grain size), amounts of grain boundaries andother defects, and the degree of preferred grain orientation. A nearlyperfect single crystal of graphite is characterized by having a mosaicspread value of 0.2-0.4. Some of our graphene foams have a mosaic spreadvalue in this range of 0.2-0.4 when produced using a final heattreatment temperature no less than 2,500° C.

It is of significance to point out that a heat treatment temperature aslow as 500° C. is sufficient to bring the average inter-graphene spacingin GO sheets along the pore walls to below 0.4 nm, getting closer andcloser to that of natural graphite or that of a graphite single crystal.

The beauty of this approach is the notion that this GO suspensionstrategy has enabled us to re-organize, re-orient, and chemically mergethe planar graphene oxide molecules from originally different graphiteparticles or graphene sheets into a unified structure with all thegraphene planes now being larger in lateral dimensions (significantlylarger than the length and width of the graphene planes in the originalgraphite particles). A potential chemical linking mechanism isillustrated in FIG. 4. This has given rise to exceptional structuralintegrity, flexibility, high thermal conductivity and high electricalconductivity values, enabling graphene foam or film layer (containing ananode or cathode active material embedded therein) to function as acurrent collector as well. This obviates the need to have separate(additional) anode and cathode current collectors.

We claim:
 1. An electrochemical battery cell comprising an anode havinga primary anode active material, a cathode having a primary cathodeactive material, and an ion-conducting electrolyte in ionic contact withsaid anode and said cathode, wherein the cell has an initial outputvoltage, Vi, measured at 10% depth of discharge (DoD), from a lowerlimit of 0.3 volts to an upper limit of 0.8 volts, and a final outputvoltage Vf measured at a DoD no greater than 90%, wherein a voltagevariation, (Vi−Vf)/Vi, is no greater than ±10% and the specific capacitybetween Vi and Vf is no less than 100 mAh/g or 200 mAh/cm³ based on thecathode active material weight or volume, and wherein said primary anodeactive material is selected from lithium (Li), sodium (Na), potassium(K), magnesium (Mg), aluminum (Al), zinc (Zn), titanium (Ti), manganese(Mn), iron (Fe), vanadium (V), cobalt (Co), nickel (Ni), a mixturethereof, an alloy thereof, or a combination thereof, and wherein saidprimary cathode active material is selected from a metal oxide, metalphosphate, metal sulfide, or a metal or semi-metal different than saidprimary anode active material, and said metal or semi-metal in saidcathode is selected from tin (Sn), bismuth (Bi), antimony (Sb), indium(In), tellurium (Te), phosphor (P), magnesium (Mg), aluminum (Al), zinc(Zn), titanium (Ti), manganese (Mn), iron (Fe), vanadium (V), cobalt(Co), nickel (Ni), selenium (Se), a mixture thereof, an alloy thereof,or a combination thereof.
 2. The electrochemical battery cell of claim1, wherein said anode further contains graphene as a protectivematerial.
 3. The electrochemical battery cell of claim 2, wherein saidprimary anode active material is embraced by graphene sheets or embeddedin a graphene film, graphene paper, graphene mat, or graphene foam. 4.The electrochemical battery cell of claim 2, wherein said graphenecontains a pristine graphene material having less than 0.01% by weightof non-carbon elements or a non-pristine graphene material having 0.01%to 50% by weight of non-carbon elements, wherein said non-pristinegraphene is selected from graphene oxide, reduced graphene oxide,graphene fluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, boron-doped graphene,nitrogen-doped graphene, chemically functionalized graphene, or acombination thereof.
 5. The electrochemical battery cell of claim 1,wherein said primary cathode active material is embraced by graphenesheets or embedded in a graphene film, graphene paper, graphene mat, orgraphene foam.
 6. The electrochemical battery cell of claim 3, whereinsaid primary cathode active material is embraced by graphene sheets orembedded in a graphene film, graphene paper, graphene mat, or graphenefoam.
 7. The electrochemical battery cell of claim 3, wherein saidgraphene film, graphene paper, graphene mat, or graphene foam in saidanode, having said primary anode active material embedded therein, isconnected to a first battery terminal tab to function as an anodecurrent collector and there is no separate or additional anode currentcollector to support said graphene film, graphene paper, graphene mat,or graphene foam.
 8. The electrochemical battery cell of claim 5,wherein said graphene film, graphene paper, graphene mat, or graphenefoam in said cathode, having said primary cathode active materialembedded therein, is connected to a battery terminal tab to function asa cathode current collector and there is no separate or additionalcathode current collector to support said graphene film, graphene paper,graphene mat, or graphene foam.
 9. The electrochemical battery cell ofclaim 7, wherein said graphene film, graphene paper, graphene mat, orgraphene foam, in said cathode, having said primary cathode activematerial embedded therein is connected to a second battery terminal taband there is no separate or additional cathode current collector tosupport said graphene film, graphene paper, graphene mat, or graphenefoam in said cathode.
 10. The electrochemical battery cell of claim 1,further comprising an anode current collector supporting said anode or acathode current collector supporting said cathode.
 11. Theelectrochemical battery cell of claim 1, wherein the specific capacitybetween Vi and Vf is no less than 200 mAh/g or 400 mAh/cm³ based on thecathode active material weight or volume.
 12. The electrochemicalbattery cell of claim 1, wherein the specific capacity between Vi and Vfis no less than 400 mAh/g or 800 mAh/cm³ based on the cathode activematerial weight or volume.
 13. The electrochemical battery cell of claim1, wherein the specific capacity between Vi and Vf is no less than 1,000mAh/g or 2,000 mAh/cm³ based on the cathode active material weight orvolume.
 14. The electrochemical battery cell of claim 1, wherein saidprimary anode active material is Mg or Al and the primary cathode activematerial is sulfur (S), a mixture of S and Se, or sulfur bonded tographene surfaces and said electrolyte is selected from aqueous,organic, polymeric, or solid state electrolyte.
 15. The electrochemicalbattery cell of claim 1, wherein said metal oxide, metal phosphate, ormetal sulfide is selected from a tin oxide, cobalt oxide, nickel oxide,manganese oxide, vanadium oxide, iron phosphate, manganese phosphate,vanadium phosphate, transition metal sulfide, or a combination thereof.16. An electrochemical battery cell comprising an anode having a primaryanode active material, a cathode having a primary cathode activematerial, and an ion-conducting electrolyte in ionic contact with saidanode and said cathode, wherein the cell has an initial output voltage,measured at 10% depth of discharge (DoD), from a lower limit of 0.3volts to an upper limit of 0.8 volts, and a final output voltage Vfmeasured at a DoD no greater than 90%, wherein a voltage variation,(Vi−Vf)/Vi, is no greater than ±10% and the specific capacity between Viand Vf is no less than 100 mAh/g or 200 mAh/cm³ based on the cathodeactive material weight or volume, and wherein said primary anode activematerial is selected from magnesium (Mg) or aluminum (Al), a mixturethereof, an alloy thereof, or a combination thereof, and wherein saidprimary cathode active material is selected from a metal oxide, metalphosphate, metal sulfide, an inorganic material, or a metal orsemi-metal different than said primary anode active material and saidmetal or semi-metal in said cathode is selected from tin (Sn), bismuth(Bi), antimony (Sb), indium (In), tellurium (Te), phosphor (P),magnesium (Mg), aluminum (Al), zinc (Zn), titanium (Ti), manganese (Mn),iron (Fe), vanadium (V), cobalt (Co), nickel (Ni), sulfur (S), selenium(Se), a mixture thereof, an alloy thereof, or a combination thereof, andfurther wherein said electrolyte is selected from aqueous, organic,polymeric, or solid state electrolyte, not including ionic electrolyte.17. The electrochemical battery cell of claim 16, wherein said inorganicmaterial is selected from carbon sulfur, sulfur compound, lithiumpolysulfide, transition metal dichalcogenide, a transition metaltrichalcogenide, or a combination thereof.
 18. The electrochemicalbattery cell of claim 1, wherein said cathode further contains grapheneas an electrochemical property modifier to said primary cathode activematerial wherein said graphene increases a cell specific capacity orincreases or decreases a cell output voltage.
 19. The electrochemicalbattery cell of claim 16, wherein said cathode further contains grapheneas an electrochemical property modifier to said primary cathode activematerial wherein said graphene increases a cell specific capacity orincreases or decreases a cell output voltage
 20. The electrochemicalbattery cell of claim 18, wherein said primary cathode active materialis bonded to or physically supported by a surface of said graphene. 21.The electrochemical battery cell of claim 18, wherein said graphenecontain a pristine graphene material having less than 0.01% by weight ofnon-carbon elements or a non-pristine graphene material having 0.01% to50% by weight of non-carbon elements, wherein said non-pristine grapheneis selected from graphene oxide, reduced graphene oxide, graphenefluoride, graphene chloride, graphene bromide, graphene iodide,hydrogenated graphene, nitrogenated graphene, boron-doped graphene,nitrogen-doped graphene, chemically functionalized graphene, or acombination thereof.
 22. The electrochemical battery cell of claim 1,wherein the voltage variation, (Vi−Vf)/Vi, is no greater than ±5%. 23.An electronic device containing the electrochemical battery cell ofclaim 1 as a power source.
 24. The electronic device of claim 23, whichcontains a sensor, an actuator, a wireless device, a wearable device, ora medical device electronically connected to said electrochemicalbattery cell.